Tag Archives: Sync

A serverless solution for invoking AWS Lambda at a sub-minute frequency

Post Syndicated from Emanuele Menga original https://aws.amazon.com/blogs/architecture/a-serverless-solution-for-invoking-aws-lambda-at-a-sub-minute-frequency/

If you’ve used Amazon CloudWatch Events to schedule the invocation of a Lambda function at regular intervals, you may have noticed that the highest frequency possible is one invocation per minute. However, in some cases, you may need to invoke Lambda more often than that. In this blog post, I’ll cover invoking a Lambda function every 10 seconds, but with some simple math you can change to whatever interval you like.

To achieve this, I’ll show you how to leverage Step Functions and Amazon Kinesis Data Streams.

The Solution

For this example, I’ve created a Step Functions State Machine that invokes our Lambda function 6 times, 10 seconds apart. Such State Machine is then executed once per minute by a CloudWatch Events Rule. This state machine is then executed once per minute by an Amazon CloudWatch Events rule. Finally, the Kinesis Data Stream triggers our Lambda function for each record inserted. The result is our Lambda function being invoked every 10 seconds, indefinitely.

Below is a diagram illustrating how the various services work together.

Step 1: My sampleLambda function doesn’t actually do anything, it just simulates an execution for a few seconds. This is the (Python) code of my dummy function:

import time

import random

def lambda_handler(event, context):

rand = random.randint(1, 3)

print('Running for {} seconds'.format(rand))


return True

Step 2:

The next step is to create a second Lambda function, that I called Iterator, which has two duties:

  • It keeps track of the current number of iterations, since Step Function doesn’t natively have a state we can use for this purpose.
  • It asynchronously invokes our Lambda function at every loops.

This is the code of the Iterator, adapted from here.


import boto3

client = boto3.client('kinesis')

def lambda_handler(event, context):

index = event['iterator']['index'] + 1

response = client.put_record(





return {

'index': index,

'continue': index < event['iterator']['count'],

'count': event['iterator']['count']


This function does three things:

  • Increments the counter.
  • Verifies if we reached a count of (in this example) 6.
  • Sends an empty record to the Kinesis Stream.

Now we can create the Step Functions State Machine; the definition is, again, adapted from here.



"Comment": "Invoke Lambda every 10 seconds",

"StartAt": "ConfigureCount",

"States": {

"ConfigureCount": {

"Type": "Pass",

"Result": {

"index": 0,

"count": 6


"ResultPath": "$.iterator",

"Next": "Iterator"


"Iterator": {

"Type": "Task",

"Resource": “arn:aws:lambda:REGION:ACCOUNT_ID:function:Iterator",

"ResultPath": "$.iterator",

"Next": "IsCountReached"


"IsCountReached": {

"Type": "Choice",

"Choices": [


"Variable": "$.iterator.continue",

"BooleanEquals": true,

"Next": "Wait"



"Default": "Done"


"Wait": {

"Type": "Wait",

"Seconds": 10,

"Next": "Iterator"


"Done": {

"Type": "Pass",

"End": true




This is how it works:

  1. The state machine starts and sets the index at 0 and the count at 6.
  2. Iterator function is invoked.
  3. If the iterator function reached the end of the loop, the IsCountReached state terminates the execution, otherwise the machine waits for 10 seconds.
  4. The machine loops back to the iterator.

Step 3: Create an Amazon CloudWatch Events rule scheduled to trigger every minute and add the state machine as its target. I’ve actually prepared an Amazon CloudFormation template that creates the whole stack and starts the Lambda invocations, you can find it here.


Let’s have a look at a sample series of invocations and analyse how precise the timing is. In the following chart I reported the delay (in excess of the expected 10-second-wait) of 30 consecutive invocations of my dummy function, when the Iterator is configured with a memory size of 1024MB.

Invocations Delay

Notice the delay increases by a few hundred milliseconds at every invocation. The good news is it accrues only within the same loop, 6 times; after that, a new CloudWatch Events kicks in and it resets.

This delay  is due to the work that AWS Step Function does outside of the Wait state, the main component of which is the Iterator function itself, that runs synchronously in the state machine and therefore adds up its duration to the 10-second-wait.

As we can easily imagine, the memory size of the Iterator Lambda function does make a difference. Here are the Average and Maximum duration of the function with 256MB, 512MB, 1GB and 2GB of memory.

Average Duration

Maximum Duration

Given those results, I’d say that a memory of 1024MB is a good compromise between costs and performance.


As mentioned, in our Amazon CloudWatch Events documentation, in rare cases a rule can be triggered twice, causing two parallel executions of the state machine. If that is a concern, we can add a task state at the beginning of the state machine that checks if any other executions are currently running. If the outcome is positive, then a choice state can immediately terminate the flow. Since the state machine is invoked every 60 seconds and runs for about 50, it is safe to assume that executions should all be sequential and any parallel executions should be treated as duplicates. The task state that checks for current running executions can be a Lambda function similar to the following:


import boto3

client = boto3.client('stepfunctions')

def lambda_handler(event, context):

response = client.list_executions(




return {

'alreadyRunning': len(response['executions']) > 0


About the Author

Emanuele Menga, Cloud Support Engineer


Securing Your Cryptocurrency

Post Syndicated from Roderick Bauer original https://www.backblaze.com/blog/backing-up-your-cryptocurrency/

Securing Your Cryptocurrency

In our blog post on Tuesday, Cryptocurrency Security Challenges, we wrote about the two primary challenges faced by anyone interested in safely and profitably participating in the cryptocurrency economy: 1) make sure you’re dealing with reputable and ethical companies and services, and, 2) keep your cryptocurrency holdings safe and secure.

In this post, we’re going to focus on how to make sure you don’t lose any of your cryptocurrency holdings through accident, theft, or carelessness. You do that by backing up the keys needed to sell or trade your currencies.

$34 Billion in Lost Value

Of the 16.4 million bitcoins said to be in circulation in the middle of 2017, close to 3.8 million may have been lost because their owners no longer are able to claim their holdings. Based on today’s valuation, that could total as much as $34 billion dollars in lost value. And that’s just bitcoins. There are now over 1,500 different cryptocurrencies, and we don’t know how many of those have been misplaced or lost.

Now that some cryptocurrencies have reached (at least for now) staggering heights in value, it’s likely that owners will be more careful in keeping track of the keys needed to use their cryptocurrencies. For the ones already lost, however, the owners have been separated from their currencies just as surely as if they had thrown Benjamin Franklins and Grover Clevelands over the railing of a ship.

The Basics of Securing Your Cryptocurrencies

In our previous post, we reviewed how cryptocurrency keys work, and the common ways owners can keep track of them. A cryptocurrency owner needs two keys to use their currencies: a public key that can be shared with others is used to receive currency, and a private key that must be kept secure is used to spend or trade currency.

Many wallets and applications allow the user to require extra security to access them, such as a password, or iris, face, or thumb print scan. If one of these options is available in your wallets, take advantage of it. Beyond that, it’s essential to back up your wallet, either using the backup feature built into some applications and wallets, or manually backing up the data used by the wallet. When backing up, it’s a good idea to back up the entire wallet, as some wallets require additional private data to operate that might not be apparent.

No matter which backup method you use, it is important to back up often and have multiple backups, preferable in different locations. As with any valuable data, a 3-2-1 backup strategy is good to follow, which ensures that you’ll have a good backup copy if anything goes wrong with one or more copies of your data.

One more caveat, don’t reuse passwords. This applies to all of your accounts, but is especially important for something as critical as your finances. Don’t ever use the same password for more than one account. If security is breached on one of your accounts, someone could connect your name or ID with other accounts, and will attempt to use the password there, as well. Consider using a password manager such as LastPass or 1Password, which make creating and using complex and unique passwords easy no matter where you’re trying to sign in.

Approaches to Backing Up Your Cryptocurrency Keys

There are numerous ways to be sure your keys are backed up. Let’s take them one by one.

1. Automatic backups using a backup program

If you’re using a wallet program on your computer, for example, Bitcoin Core, it will store your keys, along with other information, in a file. For Bitcoin Core, that file is wallet.dat. Other currencies will use the same or a different file name and some give you the option to select a name for the wallet file.

To back up the wallet.dat or other wallet file, you might need to tell your backup program to explicitly back up that file. Users of Backblaze Backup don’t have to worry about configuring this, since by default, Backblaze Backup will back up all data files. You should determine where your particular cryptocurrency, wallet, or application stores your keys, and make sure the necessary file(s) are backed up if your backup program requires you to select which files are included in the backup.

Backblaze B2 is an option for those interested in low-cost and high security cloud storage of their cryptocurrency keys. Backblaze B2 supports 2-factor verification for account access, works with a number of apps that support automatic backups with encryption, error-recovery, and versioning, and offers an API and command-line interface (CLI), as well. The first 10GB of storage is free, which could be all one needs to store encrypted cryptocurrency keys.

2. Backing up by exporting keys to a file

Apps and wallets will let you export your keys from your app or wallet to a file. Once exported, your keys can be stored on a local drive, USB thumb drive, DAS, NAS, or in the cloud with any cloud storage or sync service you wish. Encrypting the file is strongly encouraged — more on that later. If you use 1Password or LastPass, or other secure notes program, you also could store your keys there.

3. Backing up by saving a mnemonic recovery seed

A mnemonic phrase, mnemonic recovery phrase, or mnemonic seed is a list of words that stores all the information needed to recover a cryptocurrency wallet. Many wallets will have the option to generate a mnemonic backup phrase, which can be written down on paper. If the user’s computer no longer works or their hard drive becomes corrupted, they can download the same wallet software again and use the mnemonic recovery phrase to restore their keys.

The phrase can be used by anyone to recover the keys, so it must be kept safe. Mnemonic phrases are an excellent way of backing up and storing cryptocurrency and so they are used by almost all wallets.

A mnemonic recovery seed is represented by a group of easy to remember words. For example:

eye female unfair moon genius pipe nuclear width dizzy forum cricket know expire purse laptop scale identify cube pause crucial day cigar noise receive

The above words represent the following seed:

0a5b25e1dab6039d22cd57469744499863962daba9d2844243fec 9c0313c1448d1a0b2cd9e230a78775556f9b514a8be45802c2808e fd449a20234e9262dfa69

These words have certain properties:

  • The first four letters are enough to unambiguously identify the word.
  • Similar words are avoided (such as: build and built).

Bitcoin and most other cryptocurrencies such as Litecoin, Ethereum, and others use mnemonic seeds that are 12 to 24 words long. Other currencies might use different length seeds.

4. Physical backups — Paper, Metal

Some cryptocurrency holders believe that their backup, or even all their cryptocurrency account information, should be stored entirely separately from the internet to avoid any risk of their information being compromised through hacks, exploits, or leaks. This type of storage is called “cold storage.” One method of cold storage involves printing out the keys to a piece of paper and then erasing any record of the keys from all computer systems. The keys can be entered into a program from the paper when needed, or scanned from a QR code printed on the paper.

Printed public and private keys

Printed public and private keys

Some who go to extremes suggest separating the mnemonic needed to access an account into individual pieces of paper and storing those pieces in different locations in the home or office, or even different geographical locations. Some say this is a bad idea since it could be possible to reconstruct the mnemonic from one or more pieces. How diligent you wish to be in protecting these codes is up to you.

Mnemonic recovery phrase booklet

Mnemonic recovery phrase booklet

There’s another option that could make you the envy of your friends. That’s the CryptoSteel wallet, which is a stainless steel metal case that comes with more than 250 stainless steel letter tiles engraved on each side. Codes and passwords are assembled manually from the supplied part-randomized set of tiles. Users are able to store up to 96 characters worth of confidential information. Cryptosteel claims to be fireproof, waterproof, and shock-proof.

image of a Cryptosteel cold storage device

Cryptosteel cold wallet

Of course, if you leave your Cryptosteel wallet in the pocket of a pair of ripped jeans that gets thrown out by the housekeeper, as happened to the character Russ Hanneman on the TV show Silicon Valley in last Sunday’s episode, then you’re out of luck. That fictional billionaire investor lost a USB drive with $300 million in cryptocoins. Let’s hope that doesn’t happen to you.

Encryption & Security

Whether you store your keys on your computer, an external disk, a USB drive, DAS, NAS, or in the cloud, you want to make sure that no one else can use those keys. The best way to handle that is to encrypt the backup.

With Backblaze Backup for Windows and Macintosh, your backups are encrypted in transmission to the cloud and on the backup server. Users have the option to add an additional level of security by adding a Personal Encryption Key (PEK), which secures their private key. Your cryptocurrency backup files are secure in the cloud. Using our web or mobile interface, previous versions of files can be accessed, as well.

Our object storage cloud offering, Backblaze B2, can be used with a variety of applications for Windows, Macintosh, and Linux. With B2, cryptocurrency users can choose whichever method of encryption they wish to use on their local computers and then upload their encrypted currency keys to the cloud. Depending on the client used, versioning and life-cycle rules can be applied to the stored files.

Other backup programs and systems provide some or all of these capabilities, as well. If you are backing up to a local drive, it is a good idea to encrypt the local backup, which is an option in some backup programs.

Address Security

Some experts recommend using a different address for each cryptocurrency transaction. Since the address is not the same as your wallet, this means that you are not creating a new wallet, but simply using a new identifier for people sending you cryptocurrency. Creating a new address is usually as easy as clicking a button in the wallet.

One of the chief advantages of using a different address for each transaction is anonymity. Each time you use an address, you put more information into the public ledger (blockchain) about where the currency came from or where it went. That means that over time, using the same address repeatedly could mean that someone could map your relationships, transactions, and incoming funds. The more you use that address, the more information someone can learn about you. For more on this topic, refer to Address reuse.

Note that a downside of using a paper wallet with a single key pair (type-0 non-deterministic wallet) is that it has the vulnerabilities listed above. Each transaction using that paper wallet will add to the public record of transactions associated with that address. Newer wallets, i.e. “deterministic” or those using mnemonic code words support multiple addresses and are now recommended.

There are other approaches to keeping your cryptocurrency transaction secure. Here are a couple of them.


Multi-signature refers to requiring more than one key to authorize a transaction, much like requiring more than one key to open a safe. It is generally used to divide up responsibility for possession of cryptocurrency. Standard transactions could be called “single-signature transactions” because transfers require only one signature — from the owner of the private key associated with the currency address (public key). Some wallets and apps can be configured to require more than one signature, which means that a group of people, businesses, or other entities all must agree to trade in the cryptocurrencies.

Deep Cold Storage

Deep cold storage ensures the entire transaction process happens in an offline environment. There are typically three elements to deep cold storage.

First, the wallet and private key are generated offline, and the signing of transactions happens on a system not connected to the internet in any manner. This ensures it’s never exposed to a potentially compromised system or connection.

Second, details are secured with encryption to ensure that even if the wallet file ends up in the wrong hands, the information is protected.

Third, storage of the encrypted wallet file or paper wallet is generally at a location or facility that has restricted access, such as a safety deposit box at a bank.

Deep cold storage is used to safeguard a large individual cryptocurrency portfolio held for the long term, or for trustees holding cryptocurrency on behalf of others, and is possibly the safest method to ensure a crypto investment remains secure.

Keep Your Software Up to Date

You should always make sure that you are using the latest version of your app or wallet software, which includes important stability and security fixes. Installing updates for all other software on your computer or mobile device is also important to keep your wallet environment safer.

One Last Thing: Think About Your Testament

Your cryptocurrency funds can be lost forever if you don’t have a backup plan for your peers and family. If the location of your wallets or your passwords is not known by anyone when you are gone, there is no hope that your funds will ever be recovered. Taking a bit of time on these matters can make a huge difference.

To the Moon*

Are you comfortable with how you’re managing and backing up your cryptocurrency wallets and keys? Do you have a suggestion for keeping your cryptocurrencies safe that we missed above? Please let us know in the comments.

*To the Moon — Crypto slang for a currency that reaches an optimistic price projection.

The post Securing Your Cryptocurrency appeared first on Backblaze Blog | Cloud Storage & Cloud Backup.

Security updates for Wednesday

Post Syndicated from ris original https://lwn.net/Articles/754021/rss

Security updates have been issued by Debian (kernel), Gentoo (rsync), openSUSE (Chromium), Oracle (kernel), Red Hat (kernel and kernel-rt), Scientific Linux (kernel), SUSE (kernel and php7), and Ubuntu (dpdk, libraw, linux, linux-lts-trusty, linux-snapdragon, and webkit2gtk).

What’s new in HiveMQ 3.4

Post Syndicated from The HiveMQ Team original https://www.hivemq.com/whats-new-in-hivemq-3-4

We are pleased to announce the release of HiveMQ 3.4. This version of HiveMQ is the most resilient and advanced version of HiveMQ ever. The main focus in this release was directed towards addressing the needs for the most ambitious MQTT deployments in the world for maximum performance and resilience for millions of concurrent MQTT clients. Of course, deployments of all sizes can profit from the improvements in the latest and greatest HiveMQ.

This version is a drop-in replacement for HiveMQ 3.3 and of course supports rolling upgrades with zero-downtime.

HiveMQ 3.4 brings many features that your users, administrators and plugin developers are going to love. These are the highlights:


New HiveMQ 3.4 features at a glance


HiveMQ 3.4 brings various improvements in terms of scalability, availability, resilience and observability for the cluster mechanism. Many of the new features remain under the hood, but several additions stand out:

Cluster Overload Protection

The new version has a first-of-its-kind Cluster Overload Protection. The whole cluster is able to spot MQTT clients that cause overload on nodes or the cluster as a whole and protects itself from the overload. This mechanism also protects the deployment from cascading failures due to slow or failing underlying hardware (as sometimes seen on cloud providers). This feature is enabled by default and you can learn more about the mechanism in our documentation.

Dynamic Replicates

HiveMQ’s sophisticated cluster mechanism is able to scale in a linear fashion due to extremely efficient and true data distribution mechanics based on a configured replication factor. The most important aspect of every cluster is availability, which is achieved by having eventual consistency functions in place for edge cases. The 3.4 version adds dynamic replicates to the cluster so even the most challenging edge cases involving network splits don’t lead to the sacrifice of consistency for the most important MQTT operations.

Node Stress Level Metrics

All MQTT cluster nodes are now aware of their own stress level and the stress levels of other cluster members. While all stress mitigation is handled internally by HiveMQ, experienced operators may want to monitor the individual node’s stress level (e.g with Grafana) in order to start investigating what caused the increase of load.


Operators worldwide love the HiveMQ WebUI introduced with HiveMQ 3.3. We gathered all the fantastic feedback from our users and polished the WebUI, so it’s even more useful for day-to-day broker operations and remote debugging of MQTT clients. The most important changes and additions are:

Trace Recording Download

The unique Trace Recordings functionality is without doubt a lifesaver when the behavior of individual MQTT clients needs further investigation as all interactions with the broker can be traced — at runtime and at scale! Huge production deployments may accumulate multiple gigabytes of trace recordings. HiveMQ now offers a convenient way to collect all trace recordings from all nodes, zips them and allows the download via a simple button on the WebUI. Remote debugging was never easier!

Additional Client Detail Information in WebUI

The mission of the HiveMQ WebUI is to provide easy insights to the whole production MQTT cluster for operators and administrators. Individual MQTT client investigations are a piece of cake, as all available information about clients can be viewed in detail. We further added the ability to view the restrictions a concrete client has:

  • Maximum Inflight Queue Size
  • Client Offline Queue Messages Size
  • Client Offline Message Drop Strategy

Session Invalidation

MQTT persistent sessions are one of the outstanding features of the MQTT protocol specification. Sessions which do not expire but are never reused unnecessarily consume disk space and memory. Administrators can now invalidate individual session directly in the HiveMQ WebUI for client sessions, which can be deleted safely. HiveMQ 3.4 will take care and release the resources on all cluster nodes after a session was invalidated

Web UI Polishing

Most texts on the WebUI were revisited and are now clearer and crisper. The help texts also received a major overhaul and should now be more, well, helpful. In addition, many small improvements were added, which are most of the time invisible but are here to help when you need them most. For example, the WebUI now displays a warning if cluster nodes with old versions are in the cluster (which may happen if a rolling upgrade was not finished properly)

Plugin System

One of the most popular features of HiveMQ is the extensive Plugin System, which virtually enables the integration of HiveMQ to any system and allows hooking into all aspects of the MQTT lifecycle. We listened to the feedback and are pleased to announce many improvements, big and small, for the Plugin System:

Client Session Time-to-live for individual clients

HiveMQ 3.3 offered a global configuration for setting the Time-To-Live for MQTT sessions. With the advent of HiveMQ 3.4, users can now programmatically set Time-To-Live values for individual MQTT clients and can discard a MQTT session immediately.

Individual Inflight Queues

While the Inflight Queue configuration is typically sufficient in the HiveMQ default configuration, there are some use cases that require the adjustment of this configuration. It’s now possible to change the Inflight Queue size for individual clients via the Plugin System.

Plugin Service Overload Protection

The HiveMQ Plugin System is a power-user tool and it’s possible to do unbelievably useful modifications as well as putting major stress on the system as a whole if the programmer is not careful. In order to protect the HiveMQ instances from accidental overload, a Plugin Service Overload Protection can be configured. This rate limits the Plugin Service usage and gives feedback to the application programmer in case the rate limit is exceeded. This feature is disabled by default but we strongly recommend updating your plugins to profit from this feature.

Session Attribute Store putIfNewer

This is one of the small bits you almost never need but when you do, you’re ecstatic for being able to use it. The Session Attribute Store now offers methods to put values, if the values you want to put are newer or fresher than the values already written. This is extremely useful, if multiple cluster nodes want to write to the Session Attribute Store simultaneously, as this guarantees that outdated values can no longer overwrite newer values.

Disconnection Timestamp for OnDisconnectCallback

As the OnDisconnectCallback is executed asynchronously, the client might already be gone when the callback is executed. It’s now easy to obtain the exact timestamp when a MQTT client disconnected, even if the callback is executed later on. This feature might be very interesting for many plugin developers in conjunction with the Session Attribute Store putIfNewer functionality.


We ❤️ Operators and we strive to provide all the tools needed for operating and administrating a MQTT broker cluster at scale in any environment. A key strategy for successful operations of any system is monitoring. We added some interesting new metrics you might find useful.

System Metrics

In addition to JVM Metrics, HiveMQ now also gathers Operating System Metrics for Linux Systems. So HiveMQ is able to see for itself how the operating system views the process, including native memory, the real CPU usage, and open file usage. These metrics are particularly useful, if you don’t have a monitoring agent for Linux systems setup. All metrics can be found here.

Client Disconnection Metrics

The reality of many MQTT scenarios is that not all clients are able to disconnect gracefully by sending MQTT DISCONNECT messages. HiveMQ now also exposes metrics about clients that disconnected by closing the TCP connection instead of sending a DISCONNECT packet first. This is especially useful for monitoring, if you regularly deal with clients that don’t have a stable connection to the MQTT brokers.


JMX enabled by default

JMX, the Java Monitoring Extension, is now enabled by default. Many HiveMQ operators use Application Performance Monitoring tools, which are able to hook into the metrics via JMX or use plain JMX for on-the-fly debugging. While we recommend to use official off-the-shelf plugins for monitoring, it’s now easier than ever to just use JMX if other solutions are not available to you.

Other notable improvements

The 3.4 release of HiveMQ is full of hidden gems and improvements. While it would be too much to highlight all small improvements, these notable changes stand out and contribute to the best HiveMQ release ever.

Topic Level Distribution Configuration

Our recommendation for all huge deployments with millions of devices is: Start with separate topic prefixes by bringing the dynamic topic parts directly to the beginning. The reality is that many customers have topics that are constructed like the following: “devices/{deviceId}/status”. So what happens is that all topics in this example start with a common prefix, “devices”, which is the first topic level. Unfortunately the first topic level doesn’t include a dynamic topic part. In order to guarantee the best scalability of the cluster and the best performance of the topic tree, customers can now configure how many topic levels are used for distribution. In the example outlined here, a topic level distribution of 2 would be perfect and guarantees the best scalability.

Mass disconnect performance improvements

Mass disconnections of MQTT clients can happen. This might be the case when e.g. a load balancer in front of the MQTT broker cluster drops the connections or if a mobile carrier experiences connectivity problems. Prior to HiveMQ 3.4, mass disconnect events caused stress on the cluster. Mass disconnect events are now massively optimized and even tens of millions of connection losses at the same time won’t bring the cluster into stress situations.


Replication Performance Improvements

Due to the distributed nature of a HiveMQ, data needs to be replicated across the cluster in certain events, e.g. when cluster topology changes occur. There are various internal improvements in HiveMQ version 3.4, which increase the replication performance significantly. Our engineers put special love into the replication of Queued Messages, which is now faster than ever, even for multiple millions of Queued Messages that need to be transferred across the cluster.

Updated Native SSL Libraries

The Native SSL Integration of HiveMQ was updated to the newest BoringSSL version. This results in better performance and increased security. In case you’re using SSL and you are not yet using the native SSL integration, we strongly recommend to give it a try, more than 40% performance improvement can be observed for most deployments.


Improvements for Java 9

While Java 9 was already supported for older HiveMQ versions, HiveMQ 3.4 has full-blown Java 9 support. The minimum Java version still remains Java 7, although we strongly recommend to use Java 8 or newer for the best performance of HiveMQ.

Security updates for Thursday

Post Syndicated from jake original https://lwn.net/Articles/753457/rss

Security updates have been issued by CentOS (firefox, java-1.7.0-openjdk, java-1.8.0-openjdk, librelp, patch, and python-paramiko), Debian (kernel and quassel), Gentoo (chromium, hesiod, and python), openSUSE (corosync, dovecot22, libraw, patch, and squid), Oracle (java-1.7.0-openjdk), Red Hat (go-toolset-7 and go-toolset-7-golang, java-1.7.0-openjdk, and rh-php70-php), and SUSE (corosync and patch).

Converting a Kodak Box Brownie into a digital camera

Post Syndicated from Rob Zwetsloot original https://www.raspberrypi.org/blog/kodak-brownie-camera/

In this article from The MagPi issue 69, David Crookes explains how Daniel Berrangé took an old Kodak Brownie from the 1950s and turned it into a quirky digital camera. Get your copy of The MagPi magazine in stores now, or download it as a free PDF here.

Daniel Berrangé Kodak Brownie Raspberry Pi Camera

The Kodak Box Brownie

When Kodak unveiled its Box Brownie in 1900, it did so with the slogan ‘You press the button, we do the rest.’ The words referred to the ease-of-use of what was the world’s first mass-produced camera. But it could equally apply to Daniel Berrangé’s philosophy when modifying it for the 21st century. “I wanted to use the Box Brownie’s shutter button to trigger image capture, and make it simple to use,” he tells us.

Daniel Berrangé Kodak Brownie Raspberry Pi Camera

Daniel’s project grew from a previous effort in which he placed a pinhole webcam inside a ladies’ powder compact case. “The Box Brownie project is essentially a repeat of that design but with a normal lens instead of a pinhole, a real camera case, and improved software to enable a shutter button. Ideally, it would look unchanged from when it was shooting film.”

Webcam woes

At first, Daniel looked for a cheap webcam, intending to spend no more than the price of a Pi Zero. This didn’t work out too well. “The low-light performance of the webcam was not sufficient to make a pinhole camera so I just decided to make a ‘normal’ digital camera instead,” he reveals.
To that end, he began removing some internal components from the Box Brownie. “With the original lens removed, the task was to position the webcam’s electronic light sensor (the CCD) and lens as close to the front of the camera as possible,” Daniel explains. “In the end, the CCD was about 15 mm away from the front aperture of the camera, giving a field of view that was approximately the same as the unmodified camera would achieve.”

Daniel Berrangé Kodak Brownie Raspberry Pi Camera
Daniel Berrangé Kodak Brownie Raspberry Pi Camera
Daniel Berrangé Kodak Brownie Raspberry Pi Camera

It was then time for him to insert the Raspberry Pi, upon which was a custom ‘init’ binary that loads a couple of kernel modules to run the webcam, mount the microSD file system, and launch the application binary. Here, Daniel found he was in luck. “I’d noticed that the size of a 620 film spool (63 mm) was effectively the same as the width of a Raspberry Pi Zero (65 mm), so it could be held in place between the film spool grips,” he recalls. “It was almost as if it was designed with this in mind.”

Shutter success

In order to operate the camera, Daniel had to work on the shutter button. “The Box Brownie’s shutter button is entirely mechanical, driven by a handful of levers and springs,” Daniel explains. “First, the Pi Zero needs to know when the shutter button is pressed and second, the physical shutter has to be open while the webcam is capturing the image. Rather than try to synchronise image capture with the fraction of a second that the physical shutter is open, a bit of electrical tape was used on the shutter mechanism to keep it permanently open.”

Daniel Berrangé Kodak Brownie Raspberry Pi Camera

Daniel made use of the Pi Zero’s GPIO pins to detect the pressing of the shutter button. It determines if each pin is at 0 or 5 volts. “My thought was that I could set a GPIO pin high to 5 V, and then use the action of the shutter button to short it to ground, and detect this change in level from software.”

This initially involved using a pair of bare wires and some conductive paint, although the paint was later replaced by a piece of tinfoil. But with the button pressed, the GPIO pin level goes to zero and the device constantly captures still images until the button is released. All that’s left to do is smile and take the perfect snap.

The post Converting a Kodak Box Brownie into a digital camera appeared first on Raspberry Pi.

[$] PostgreSQL visits LSFMM

Post Syndicated from jake original https://lwn.net/Articles/752952/rss

The recent fsync() woes
experienced by
PostgreSQL led to a session on the first
day (April 23) of the 2108 Linux
Storage, Filesystem, and Memory-Management Summit (LSFMM). Those problems
also led
to a second-day session with PostgreSQL developer Andres Freund who gave an
overview of how PostgreSQL does I/O and where that ran aground on some
assumptions that had been made. The session led to a fair amount of
discussion with the filesystem-track developers; real solutions seem to be
in the offing.

Security updates for Tuesday

Post Syndicated from ris original https://lwn.net/Articles/753257/rss

Security updates have been issued by Fedora (cups-filters, ghostscript, glusterfs, PackageKit, qpdf, and xen), Mageia (anki, libofx, ming, sox, webkit2, and xdg-user-dirs), Oracle (corosync, java-1.7.0-openjdk, and pcs), Red Hat (java-1.7.0-openjdk), Scientific Linux (corosync, firefox, gcc, glibc, golang, java-1.7.0-openjdk, java-1.8.0-openjdk, kernel, krb5, librelp, libvncserver, libvorbis, ntp, openssh, openssl, PackageKit, patch, pcs, policycoreutils, qemu-kvm, and xdg-user-dirs), Slackware (libwmf and mozilla), and Ubuntu (apache2, ghostscript, mysql-5.7, wavpack, and webkit2gtk).

[$] PostgreSQL’s fsync() surprise

Post Syndicated from corbet original https://lwn.net/Articles/752063/rss

Developers of database management systems are, by necessity, concerned
about getting data safely to persistent storage. So when the PostgreSQL
community found out that the way the kernel handles I/O errors could result
in data being lost without any errors being reported to user space, a fair
amount of unhappiness resulted. The problem, which is exacerbated by the
way PostgreSQL performs buffered I/O, turns out not to be unique to Linux,
and will not be easy to solve even there.

Security updates for Wednesday

Post Syndicated from ris original https://lwn.net/Articles/752183/rss

Security updates have been issued by Debian (freeplane and jruby), Fedora (kernel and python-bleach), Gentoo (evince, gdk-pixbuf, and ncurses), openSUSE (kernel), Oracle (gcc, glibc, kernel, krb5, ntp, openssh, openssl, policycoreutils, qemu-kvm, and xdg-user-dirs), Red Hat (corosync, glusterfs, kernel, and kernel-rt), SUSE (openssl), and Ubuntu (openssl and perl).

Achieving Major Stability and Performance Improvements in Yahoo Mail with a Novel Redux Architecture

Post Syndicated from mikesefanov original https://yahooeng.tumblr.com/post/173062946866


By Mohit Goenka, Gnanavel Shanmugam, and Lance Welsh

At Yahoo Mail, we’re constantly striving to upgrade our product experience. We do this not only by adding new features based on our members’ feedback, but also by providing the best technical solutions to power the most engaging experiences. As such, we’ve recently introduced a number of novel and unique revisions to the way in which we use Redux that have resulted in significant stability and performance improvements. Developers may find our methods useful in achieving similar results in their apps.

Improvements to product metrics

Last year Yahoo Mail implemented a brand new architecture using Redux. Since then, we have transformed the overall architecture to reduce latencies in various operations, reduce JavaScript exceptions, and better synchronized states. As a result, the product is much faster and more stable.

Stability improvements:

  • when checking for new emails – 20%
  • when reading emails – 30%
  • when sending emails – 20%

Performance improvements:

  • 10% improvement in page load performance
  • 40% improvement in frame rendering time

We have also reduced API calls by approximately 20%.

How we use Redux in Yahoo Mail

Redux architecture is reliant on one large store that represents the application state. In a Redux cycle, action creators dispatch actions to change the state of the store. React Components then respond to those state changes. We’ve made some modifications on top of this architecture that are atypical in the React-Redux community.

For instance, when fetching data over the network, the traditional methodology is to use Thunk middleware. Yahoo Mail fetches data over the network from our API. Thunks would create an unnecessary and undesirable dependency between the action creators and our API. If and when the API changes, the action creators must then also change. To keep these concerns separate we dispatch the action payload from the action creator to store them in the Redux state for later processing by “action syncers”. Action syncers use the payload information from the store to make requests to the API and process responses. In other words, the action syncers form an API layer by interacting with the store. An additional benefit to keeping the concerns separate is that the API layer can change as the backend changes, thereby preventing such changes from bubbling back up into the action creators and components. This also allowed us to optimize the API calls by batching, deduping, and processing the requests only when the network is available. We applied similar strategies for handling other side effects like route handling and instrumentation. Overall, action syncers helped us to reduce our API calls by ~20% and bring down API errors by 20-30%.

Another change to the normal Redux architecture was made to avoid unnecessary props. The React-Redux community has learned to avoid passing unnecessary props from high-level components through multiple layers down to lower-level components (prop drilling) for rendering. We have introduced action enhancers middleware to avoid passing additional unnecessary props that are purely used when dispatching actions. Action enhancers add data to the action payload so that data does not have to come from the component when dispatching the action. This avoids the component from having to receive that data through props and has improved frame rendering by ~40%. The use of action enhancers also avoids writing utility functions to add commonly-used data to each action from action creators.


In our new architecture, the store reducers accept the dispatched action via action enhancers to update the state. The store then updates the UI, completing the action cycle. Action syncers then initiate the call to the backend APIs to synchronize local changes.


Our novel use of Redux in Yahoo Mail has led to significant user-facing benefits through a more performant application. It has also reduced development cycles for new features due to its simplified architecture. We’re excited to share our work with the community and would love to hear from anyone interested in learning more.

AWS AppSync – Production-Ready with Six New Features

Post Syndicated from Jeff Barr original https://aws.amazon.com/blogs/aws/aws-appsync-production-ready-with-six-new-features/

If you build (or want to build) data-driven web and mobile apps and need real-time updates and the ability to work offline, you should take a look at AWS AppSync. Announced in preview form at AWS re:Invent 2017 and described in depth here, AWS AppSync is designed for use in iOS, Android, JavaScript, and React Native apps. AWS AppSync is built around GraphQL, an open, standardized query language that makes it easy for your applications to request the precise data that they need from the cloud.

I’m happy to announce that the preview period is over and that AWS AppSync is now generally available and production-ready, with six new features that will simplify and streamline your application development process:

Console Log Access – You can now see the CloudWatch Logs entries that are created when you test your GraphQL queries, mutations, and subscriptions from within the AWS AppSync Console.

Console Testing with Mock Data – You can now create and use mock context objects in the console for testing purposes.

Subscription Resolvers – You can now create resolvers for AWS AppSync subscription requests, just as you can already do for query and mutate requests.

Batch GraphQL Operations for DynamoDB – You can now make use of DynamoDB’s batch operations (BatchGetItem and BatchWriteItem) across one or more tables. in your resolver functions.

CloudWatch Support – You can now use Amazon CloudWatch Metrics and CloudWatch Logs to monitor calls to the AWS AppSync APIs.

CloudFormation Support – You can now define your schemas, data sources, and resolvers using AWS CloudFormation templates.

A Brief AppSync Review
Before diving in to the new features, let’s review the process of creating an AWS AppSync API, starting from the console. I click Create API to begin:

I enter a name for my API and (for demo purposes) choose to use the Sample schema:

The schema defines a collection of GraphQL object types. Each object type has a set of fields, with optional arguments:

If I was creating an API of my own I would enter my schema at this point. Since I am using the sample, I don’t need to do this. Either way, I click on Create to proceed:

The GraphQL schema type defines the entry points for the operations on the data. All of the data stored on behalf of a particular schema must be accessible using a path that begins at one of these entry points. The console provides me with an endpoint and key for my API:

It also provides me with guidance and a set of fully functional sample apps that I can clone:

When I clicked Create, AWS AppSync created a pair of Amazon DynamoDB tables for me. I can click Data Sources to see them:

I can also see and modify my schema, issue queries, and modify an assortment of settings for my API.

Let’s take a quick look at each new feature…

Console Log Access
The AWS AppSync Console already allows me to issue queries and to see the results, and now provides access to relevant log entries.In order to see the entries, I must enable logs (as detailed below), open up the LOGS, and check the checkbox. Here’s a simple mutation query that adds a new event. I enter the query and click the arrow to test it:

I can click VIEW IN CLOUDWATCH for a more detailed view:

To learn more, read Test and Debug Resolvers.

Console Testing with Mock Data
You can now create a context object in the console where it will be passed to one of your resolvers for testing purposes. I’ll add a testResolver item to my schema:

Then I locate it on the right-hand side of the Schema page and click Attach:

I choose a data source (this is for testing and the actual source will not be accessed), and use the Put item mapping template:

Then I click Select test context, choose Create New Context, assign a name to my test content, and click Save (as you can see, the test context contains the arguments from the query along with values to be returned for each field of the result):

After I save the new Resolver, I click Test to see the request and the response:

Subscription Resolvers
Your AWS AppSync application can monitor changes to any data source using the @aws_subscribe GraphQL schema directive and defining a Subscription type. The AWS AppSync client SDK connects to AWS AppSync using MQTT over Websockets and the application is notified after each mutation. You can now attach resolvers (which convert GraphQL payloads into the protocol needed by the underlying storage system) to your subscription fields and perform authorization checks when clients attempt to connect. This allows you to perform the same fine grained authorization routines across queries, mutations, and subscriptions.

To learn more about this feature, read Real-Time Data.

Batch GraphQL Operations
Your resolvers can now make use of DynamoDB batch operations that span one or more tables in a region. This allows you to use a list of keys in a single query, read records multiple tables, write records in bulk to multiple tables, and conditionally write or delete related records across multiple tables.

In order to use this feature the IAM role that you use to access your tables must grant access to DynamoDB’s BatchGetItem and BatchPutItem functions.

To learn more, read the DynamoDB Batch Resolvers tutorial.

CloudWatch Logs Support
You can now tell AWS AppSync to log API requests to CloudWatch Logs. Click on Settings and Enable logs, then choose the IAM role and the log level:

CloudFormation Support
You can use the following CloudFormation resource types in your templates to define AWS AppSync resources:

AWS::AppSync::GraphQLApi – Defines an AppSync API in terms of a data source (an Amazon Elasticsearch Service domain or a DynamoDB table).

AWS::AppSync::ApiKey – Defines the access key needed to access the data source.

AWS::AppSync::GraphQLSchema – Defines a GraphQL schema.

AWS::AppSync::DataSource – Defines a data source.

AWS::AppSync::Resolver – Defines a resolver by referencing a schema and a data source, and includes a mapping template for requests.

Here’s a simple schema definition in YAML form:

    Type: "AWS::AppSync::GraphQLSchema"
      - AppSyncGraphQLApi
      ApiId: !GetAtt AppSyncGraphQLApi.ApiId
      Definition: |
        schema {
          query: Query
          mutation: Mutation
        type Query {
          singlePost(id: ID!): Post
          allPosts: [Post]
        type Mutation {
          putPost(id: ID!, title: String!): Post
        type Post {
          id: ID!
          title: String!

Available Now
These new features are available now and you can start using them today! Here are a couple of blog posts and other resources that you might find to be of interest: